The Fischer-Tropsch process can be used for the conversion of hydrocarbonaceous feed stocks into normally liquid and/or solid hydrocarbons (0° C., 1 bar). The feed stock (e.g. natural gas, associated gas and/or coal-bed methane, coal) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas (or syngas) is then converted in one or more steps over a suitable catalyst at elevated temperature and pressure into paraffinic compounds ranging from methane to high molecular weight molecules comprising up to 200 carbon atoms, or, under particular circumstances, even more.
The Fischer-Tropsch reaction is very exothermic and temperature sensitive. In consequence, careful temperature control is required to maintain optimum operation conditions and desired hydrocarbon product selectivity. Numerous types of reactor systems have been developed for carrying out the Fischer-Tropsch reaction. For example, Fischer-Tropsch reactor systems include fixed bed reactors, especially multi-tubular fixed bed reactors, fluidised bed reactors, such as entrained fluidised bed reactors and fixed fluidised bed reactors, and slurry bed reactors such as three-phase slurry bubble columns and ebullated bed reactors.
Further, general methods of preparing catalyst and catalyst materials and forming catalyst mixtures are known in the art, see for example U.S. Pat. Nos. 4,409,131, 5,783,607, 5,502,019, WO 0176734, CA 1166655, U.S. Pat. Nos. 5,863,856 and 5,783,604. These include preparation by co-precipitation and impregnation.
The Fischer-Tropsch reaction is very exothermic and temperature sensitive. In consequence, careful temperature control is required to maintain optimum operation conditions and desired hydrocarbon product selectivity. The fact that the reaction is very exothermic also has the consequence that when temperature control is not adequate, the reactor temperature can increase very quickly, which carries the risk of a reactor runaway. A reactor runaway may result in highly increased temperatures at one or more locations in the reactor. A high-speed stop may, for example, be required when the temperature in the Fischer-Tropsch reactor increases to an unacceptable value either locally or over the entire reactor, when there is an interruption in the gas flow, or in the case of other unforeseen circumstances. When there is a threat of a runaway, it is often wise to stop the reaction as quick as possible. A reactor runaway is a most undesirable phenomenon, as it may result in catalyst deactivation which necessitates untimely replacement of the catalyst, causing reactor downtime and additional catalyst cost. Many of the catalysts of fixed bed catalysts are aimed at surviving measurement against an occurring reactor runaway or circumstances leading to a possible runaway.
Multi-tubular reactors also suffer from pressure drop. This pressure drop is caused by a loss of pressure in a reactor or reactor tube due to the resistance a fluid encounters when flowing through the reactor or reactor tube. In case of multi-tubular reactors, pressure drop can even result in varying pressures between the different tubes.
The desired use of highly active and less diffusion limited catalysts in Fischer-Tropsch fixed-bed reactors makes the situation even more challenging. The susceptibility to a runaway increases with increased catalyst activity and with reduced diffusion limitation of the catalyst. Examples of methods that are especially suitable for Fischer-Tropsch fixed-bed reactors comprising highly active and less diffusion limited catalysts can be found in WO2010063850, WO2010069925, and WO2010069927.